On Dec. 10, a San Joaquin County social worker visited Bianca Armstead, 19, and her daughter, Raziah Bates, not quite 11 months old.

Someone had called the county's child-protection office a week earlier with concerns about the baby.

To the social worker who came to check on her, Raziah "appeared healthy and happy," according to a heavily redacted report provided to The Record in response to a Public Records Act request.

She sat in her mother's arms. She played with her aunt and her cousins, who also were in the room.

Armstead said "there was nothing currently wrong with the minor," the social worker would later write. "The minor did not cry or cringe when touched."

Still, the report indicates that before leaving, the social worker told Armstead that Raziah needed medical attention, that she would check in with the family again, and that if Raziah hadn't been seen by a doctor, the girl would be taken away.

No one from the child protection office saw Raziah after that.

Two weeks later - on Christmas Day - she died. Her mother is facing torture and murder charges.

Qua'Tisha Cummings, Armstead's sister, was there when the social worker came to see her niece.

Three days after the baby's death, and in the midst of planning a funeral, she called child protection authorities:

She "was very upset, indicating the CPS social worker told her sister, (Raziah's) mother, that she was going to check to be sure medical treatment had been sought and that if it had not, she would be back to remove the baby," according to the report.

"She feels that if the social worker had checked as promised, the baby would have been removed and still alive today."

Documents obtained by The Record from a source within the county Human Services Agency - which oversees child protection - show that the social worker assigned to Raziah Bates also was responsible for investigating at least 30 other reports of abuse or neglect.

According to social workers, that's a typical caseload in San Joaquin County. But it is far larger than what experts say is ideal for keeping children safe: as few as 10 cases per social worker, according to some research.

It was only a matter of time, several child protection professionals have told The Record, before the straining system left a child like Raziah hurt or worse.

"What killed this baby," said Michael Perez, a 16-year employee with the Human Services Agency, currently on stress-related medical leave, "is a social worker who had too many cases and not enough time."

For most of his career, Perez has supervised social workers who, like the one assigned to Raziah's case, investigate reports of abuse against children.

"Could Raziah Bates have been saved by the Human Services Agency and the community? We will never know," he said. "But at least she could have had a better chance of survival if CPS had spent more time in providing best-practice services."

Internal memos and e-mail messages, as well as public reports, describe a child welfare agency that has long been dealing with social worker caseloads larger than what experts recommend.

At the same time, reports of abuse have increased both in number and complexity. "There are multiple issues: neglect, drugs, physical abuse, sexual molestation," said one social worker who spoke on the condition that her name not be published because she fears professional reprisal.

Under state guidelines, social workers have a duty to perform timely investigations of abuse reports. Depending on the severity of the allegations, they must visit the child within hours, or within 10 days of the report. After that, they have 30 days to conduct further interviews, to research a parent's background, to visit schools and doctors, to check in with the child again - and finally to decide whether abuse occurred, and if so, what to do about it.

Agency policies on discipline and overtime seem at odds with efforts to complete those investigations thoroughly: Social workers who repeatedly fail to close investigations within the 30-day period face formal reprimand - a system that many social workers said forces them to rush labor-intensive and highly sensitive work. But requests to use overtime to manage large caseloads are rarely approved.

"Unless there are exigent circumstances, people should be doing the same amount of work as their neighbor," said John Greco, the interim deputy director for Children's Services. The department oversees child protection. Staffing levels are largely determined by how much money comes from state and federal sources.

He agreed that smaller caseloads would improve the system, but he said neither current caseload sizes nor pressure on social workers to close investigations quickly put children at risk.

But social workers who spoke to The Record - about one quarter of the staff - said they aren't spending enough time with families to recognize all potential threats.

As a result, Perez said, visits to vulnerable children are completed with good intentions, but often hastily.

"Basically, social workers have time to get in and get out," he said.

Said one social worker: "Do children get left at risk? I would like to believe, no, but the reality is, yes, they do. ... I think we are forced to close a lot of cases without knowing the kids are safe."

When someone calls in a report of abuse to the county's Child Protective Services agency, the report, known as a referral, is logged, evaluated for severity and assigned to a social worker to investigate.

Generally, social workers are not to receive more than six referrals - each of which could represent multiple children - a week.

In a September 2007 memo to child-protection staff members, David Erb, then deputy director for Children's Services, wrote, "Child Protective Services is experiencing an increase in the number of referrals and is also temporarily understaffed."

He introduced an overflow system in which social workers would sometimes be assigned more than the typical six referrals per week.

"It is expected," the memo states, "that staff will attempt to investigate the referrals during the normal course of business." Overtime would be an exception.

About two months later, in a report submitted by Erb and Human Services Agency Director Joe Chelli to the California Department of Social Services, officials wrote, "The average caseload size for ... social workers is approximately six cases per worker per week; based on the numbers of calls that come in during a given month, this number can be even higher."

In 1998, the state Legislature ordered the Department of Social Services to commission a study, in part to discover how many cases a social worker can handle and still deliver adequate protection.

The study, published in 2000, found that social workers should be spending at least nine hours on each referral, with close to 12 hours being optimal. That would limit caseloads to about 10 to 13 referrals per month.

Social workers who spoke with The Record said they continue to be assigned at least six referrals a week.

"Because you don't have the time to provide the necessary services, and you don't have the time to investigate, ... sooner or later, it's going to blow up," said Vicki Norris, who spent nearly a decade investigating abuse reports as a social worker and still works in the agency. "That's how you're going to get dead kids."

Greco disagreed. He said six referrals a week is a maximum. Usually, most social workers are not assigned that many.

At any given time, he said, there are about 24 social workers available to receive referrals countywide. From August to December, the average number of monthly assignments ranged from 12.4 referrals to 16.4 referrals per social worker, Greco said. That's still higher than recommended in the 2000 study, but well below the six-referrals-per-week average that social workers maintain is their reality.

Since March, the overflow system - in which social workers must take on more than six assignments in a given week - has been used five times: once in March, twice in May and once each in August and November, Greco said. He said overtime is automatically granted when a social worker receives an overflow assignment.

When an anonymous caller contacted Child Protective Services just before 1 p.m. on Dec. 3 to report abuse against 10-month-old Raziah Bates, it was the third time such allegations had been leveled against her mother, Bianca Armstead.

The first came March 25, when Raziah was just 2 months old. The next was on Oct. 8. Armstead would later say both were false reports.

Five days after the Dec. 3 phone call, a social worker made an unannounced visit to Armstead's Stockton home. No one answered. The worker left her business card and asked for a return phone call.

On Dec. 10, Cummings called the social worker back and said she would get a message to her sister. She did, and later that day, the social worker saw Raziah for the first and only time.

The worker left the interview with the impression that the baby was "healthy and happy." But she seemed to have been concerned enough to leave a business card with Cummings "so that she could get in touch with the social worker privately," according to a report. "(Cummings) appeared both careful and concerned during the interview; however, she did not directly indicate that she thought the mother was causing any harm to the baby."

On Dec. 16, Cummings left a telephone message for the social worker, saying that her sister had moved out of her home. The social worker returned the call Dec. 17. There was no further interaction.

Raziah was brought to the hospital on Christmas Eve. She died within 24 hours.

On Dec. 27, her social worker called medical professionals to make sure Raziah was up-to-date on immunizations and to find out if she had received medical care. The next day, she called a resource center to ask whether Armstead had sought the counseling services she had recommended.

As a supervisor, Michael Perez was tasked with disciplining social workers who failed too often to close investigations within 30 days.

Once a month, on a day known to social workers as "Black Tuesday," "Hell Tuesday" or "Killer Tuesday," supervisors would check the status of investigations and tally how many had been open longer than guidelines allow.

After one or two verbal warnings for failing to close cases on time, supervisors issue a "counseling memo," alerting social workers that they are out of compliance. If they fail again within the same 12-month period to close investigations on time, a formal letter of reprimand is issued. That letter remains in an employee's personnel file for at least two years, and, while it is there, the employee is ineligible for transfers or promotions.

Social workers said the threat of receiving a counseling memo or letter of reprimand forces them to work faster than they think they should.

In an e-mail message dated July 8, 2009, Perez was scolded for failing to issue a letter of reprimand to a social worker with too many cases open longer than 30 days.

"Did you do a letter of reprimand?" The message asks. "If so, I need a copy. If not, why not? ... Compliance is a very big issue in our program, and I need to know that all of the supervisors are following our policy 100% - including you, Michael."

About nine months later, he said, he had an anxiety attack in his office. He has been on leave since April.

"I couldn't keep cracking the whip when I knew the caseloads were impossible," he said. "My conscience finally got to me."

Bianca Armstead's most recent court appearance came on Valentine's Day, and it was brief.

A bailiff led her into the courtroom. She glanced behind her and smiled slightly at family members.

A lawyer submitted records, and a new court date was set: March 7.

Meanwhile, San Joaquin County is conducting a previously scheduled review of its child-protection system.

The first phase of that state-mandated review was finished Jan. 25, when Human Services Agency administrators delivered to county supervisors an evaluation detailing case numbers, policies and goals.

Without public discussion, supervisors signed off on the evaluation in a vote that included routine agenda items, such as a donation to the Stockton Sportsmen's Club and an employment agreement.

In coming weeks, the Human Services Agency is expected to complete the review by submitting a system improvement plan to supervisors.

Perez, who has independently compiled research on social worker caseloads and how they might have contributed to Raziah's death, said he would present his findings to supervisors when they consider the improvement plan. He said he would urge them to discuss the plan at length, and separately from routine business items, before approving it.